
If \(b \ge m+n\) , all diagonal entries of \({\bf D}\)  are almost surely
equal to 1. This case
corresponds to the conventional unitary space-time modulation
(USTM) [1]}, where \({\bf D}={\bf I}\)  and \(c=b\) ;

If \(b<m+n\) , the optimal input is \({\bf D}\sim {\cal B}_n(b-n,m+n-b)\) , which is referred to as
Beta-variate space-time modulation (BSTM) [2]}. This scenario allows the analysis of
an uplink massive-MIMO system, with \(m \ge n\)  and even \(m\gg n\) , which is relevant in the next-generation
cellular setting.

